The integrity of analog/RF circuit signal and digital circuit signals is an important factor when designing a mixed-signal circuit or a digital circuit. Three components responsible for decreasing the signal integrity of mixed-signal and digital circuits are ground noise, power supply noise, and substrate noise. As the noise from one or more of these noise sources is reduced, the integrity of mixed signal circuit and a digital circuit signals increases.
A mixed-signal circuit includes analog/RF circuits and digital circuits on the same substrate. Because the analog/RF circuits and digital circuits use a common substrate, a signal path is created between the noisy digital portion(s) and the noise-sensitive analog/RF portion(s) of the circuit. Thus, signal isolation of sensitive analog/RF circuits from the noisy digital circuits is desirable.
In digital circuits, noise on the power and ground rails has a resistive (IR drop) noise component and an inductive (L di/dt) noise component. Therefore, IR drop noise and L di/dt noise present on ground and/or power rails propagate into the substrate through substrate ties and well ties.
In modem application-specific integrated circuit (ASIC) design, each logic function (e.g., OR, NOR, AND, NAND, etc.) is represented by a “standard cell,” and the various standard cells are typically grouped together to form a “library” of standard cells. Additionally, the library usually contains multiple standard cells of the same logic function, but with differing characteristics (e.g., area, speed, power consumption, etc.).
When designing a semiconductor device, a designer may use the various cells in the library to create a desired semiconductor device. The variety of standard cells enables designers to more efficiently create semiconductor designs, and indirectly gives the designer implementation tradeoffs (e.g., area vs. speed vs. power consumption).
Though current libraries include different implementations of the same logic function, these libraries do not include reduced-noise cells (“noise-aware” cells) capable of performing the standard cell logic functions. Accordingly, it is desirable to provide semiconductor cells for reducing noise in mixed-signal and digital circuits. In addition, it is desirable to provide a method for designing a semiconductor device using a standard cell library and a noise-aware library. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.